1. Field of the Invention
The present invention relates to a microlens and its forming method being suitably used in devices for optical communications and more particularly to the microlens and its forming method being suitably applied to formation of many very fine and small diffractive optical elements such as computer-generated hologram (CGH) devices.
2. Description of the Related Art
A method for forming many microlenses each being coupled to an optical fiber is disclosed in xe2x80x9cProceeding SPIE (Vol. 3631, p234-243)xe2x80x9d issued in April 1999. According to this conventional technology, by tying many cylindrical optical elements each having an outer diameter equal to that of an optical fiber in a bundle and by performing etching processing on end faces of the optical elements using specified etching mask, many specified lens planes can be formed on an end face of each of the many optical elements in a collective manner.
By using the microlens made from such the optical element having the same outer diameter as that of the optical fiber, when the microlens is placed in a V-groove on a substrate in a manner that an end face of a lens plane faces an end of the optical fiber being also placed in the V-groove, it is possible to accurately align an optical axis of the microlens with that of the optical fiber.
However, the conventional method for forming the microlens described above has problems. That is, in the conventional method, in order to collectively form the lens plane on end faces of many optical elements, it is necessary to surely and accurately tie many optical elements in a bundle, however, it is not easy to accurately tie many optical elements in a bundle and to reliably form the lens plane on the end faces of the many optical elements.
In view of the above, it is an object of the present invention to provide a method for forming many microlens comparatively easily and effectively. It is another object of the present invention to provide a novel microlens which enables exact alignment of an optical axis of the microlens with an optical axis of the optical fiber.
According to a first aspect of the present invention, there is provided a method of forming a plurality of microlenses including the steps of:
forming a plurality of lens planes on one surface of an optical substrate;
forming a plurality of mask portions respectively on each the lens planes;
forming lens element portions which has the lens plane and becomes microlens respectively under each of the mask portions by an etching process conducted on the optical substrate;
removing all mask portions;
holding these lens element portions by a holding means from the side the one surface of the optical substrate is located;
removing a remainder of the optical substrate excluding these lens element portions for leaving these lens element portions by a removing process;
eliminating the holding means from all lens element portion by a eliminating process.
With the above configuration, after forming collectively and integrally a plurality of lens element portions each containing a lens plane by the etching process and others conducted on an optical substrate having a plurality of lens planes, separating these lens element portions by the removing process and the eliminating process. Therefore, a plurality of microlenses each made up of the lens element portions is formed easily and effectively.
In the foregoing, the etching process may be an etching processing to etch an exposure area portion being not covered by these mask portions.
Also, the etching process may contain a etching processing to etch an exposure area portion being not covered by these mask portions for forming a part of the lens element portion, a forming processing to form a protecting film on a wall surrounding face of the part formed by the etching processing, and a film removing processing conducted after all lens element portions are formed by conducting the etching processing and the forming processing repeatedly to remove the protecting film.
Also, the etching process may be conducted by using etching gas exhibiting an anisotropic etching characteristic.
With the above configuration, it is possible to provide a desired length to each microlens.
In the method, the optical substrate may be made up of a crystal substrate, the crystal substrate may be a silicon crystal substrate. When using the silicon crystal substrate, the removing process may be a polishing processing.
Also, in the method, the optical substrate may be SOI substrate. It has a silicon layer having the one surface and providing a thickness in correspondence with a length of the microlens, a silicon dioxide layer fixed on the silicon layer, and a silicon substrate layer fixed on the silicon dioxide layer. When using the SOI substrate, the removing process is a dissolving processing to dissolve said silicon dioxide layer.
In the method, the holding means may consist of a wax material layer used to fill the space between these lens element portions and covering all lens element portions, and a holding substrate fixed on the wax material layer. When using the holding means, the eliminating process is a dissolving processing to dissolve the wax material layer.
In the method, the microlens may be a diffractive optical element, in this case, the lens plane of the diffractive optical element is formed.
Also, in the method, moreover the steps may be comprised that are to form a antireflection film on each of end faces of all lens element portions which is located on an opposite side of the lens plane after finishing the removing process, to use a support means to support all lens element portions from the side all the end faces are located on which the antireflection film is formed before conducting the eliminating process, to form a antireflection film on all lens planes of all lens element portions after finishing the eliminating process, and to remove the support means from all lens element portions by conducting a support means eliminating process.
The support means may have a support substrate to support all lens element portions through UV (Ultraviolet) resin layer, said support means eliminating process is a dissolving processing to dissolve the UV resin layer.
Also, there is provided a method of forming a plurality of microlens including the steps of:
forming a plurality of lens planes on one surface of an optical substrate;
forming a plurality of mask portions respectively on each of the lens planes;
forming lens element portions which has the lens plane and becomes the microlens respectively under each of the mask portions by an etching process conducted on the optical substrate;
forming a mold by using the optical substrate as an original substrate obtained after all the mask potions are removed for reproducing the optical substrate
forming replica substrates by using the mold;
holding all lens element portions of the replica substrate by a holding means from the side one surface of the replica substrate is located;
removing a remainder of the replica substrate excluding these lens element portions for leaving these lens element portions by a removing process;
eliminating the holding means from all lens element portions by a eliminating process.
According to a second aspect of the present invention, there is provided a microlens formed by methods stated above, wherein the microlens is placed in series to face an optical fiber in a V-groove on a substrate, and it has an outer diameter in correspondence with that of said optical fiber and a lens plane facing the optical fiber.
Also, there is provided a microlens formed by a method stated above, wherein the microlens is substantially a cylindrical shape as a whole, and has one end face on which the lens plane is formed and another end face which is opposed to the one end face.
Also, there is provided an optical module including:
a microlens stated above, an optical fiber having an outer diameter being substantially same as that of the microlens, and a substrate having a groove
wherein the microlens and the optical fiber are placed in the groove in series, and the lens plane of the microlens faces one end face of the optical fiber.
Also, the groove may be V-groove.